Data Validation Error

I am attempting to do a data validation given three potential outcomes for a cell, either "2", "3", or "4". Depending on the value of the first cell, the value ranges available to me in the second cell change. I am attempting to use the formula:

=IF($D$6=2,$C$20:$C$33,IF($D$6=3,$C$35:$C$52,IF($D$6=4,$C$54:$C$74)))

as a List data validation. Sometimes the formula works, but other times I receive a message "The list source must be a delimited list, or a reference to a single row or column." I don't see why it is giving me that error.

Does anyone have any suggestions?

Thank you

At a guess, when you get the error D6 doesn't equal 2,3 or 4.

I believe I attached my file properly. You can see in cells E4 and E6 the formula works properly. In cell E5 however, when I attempt to enter the same formula and switch it from custom to a list data validation, it gives me the error message.

As per post#3 it's because D6 is empty, try

Formula:

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Awesome, thanks guys. I assumed that the formula should work even when the prior cells were blank still, I didn't realize it would want to validate D6 has 2,3,4 before allowing the formula to work. I can use my formula and then tell it to ignore blanks to ensure that E6 can't be filled until D6 is. Thank you both very much.

Glad we could help & thanks for the feedback